How to split long posts in multiple pages in twentysixteen

Question

You have to add <!–nextpage–> in Text mode of editor. If you add it through Visual editor – WP will escape it to HTML:

&lt;!--nextpage--&gt;

and display it literally (instead of pagination):

<!–nextpage–>

So, check your post by switching to Text editor. If nothing isn’t displayed at all when you view the post, this may be a plugin issue. Update your theme to the latest version and disable all plugins temporarily.